When should I inform my current group I'm leaving?

Analyst here with option to sign associate contract soon. If I tell them early that I plan on leaving in a few months (after YE bonus hits), then I'd imagine they'd give me a smaller bonus. This is a business at the end of the day, but I don't want to leave on bad terms by not saying anything until right after signing on to be an associate and collecting my bonus. What's the best way to navigate this?

For a deal-based HF, so would be leaving the team understaffed for a short while. That being said, it is a business and they can find another associate.